Electric gaseous discharge device



April 1939- E. FRIEDERICH 2, 2,993

ELECTRIC GASEOUS DISCHARGE DEVICE Filed Sept. 18, 1935 I B IU NWW INVENTOR BY 9 M 29 8 Wan? 49 RNEY Patented Apr. 4, 1939' UNITED srarss PATENT OFFICE 3,152,998 ELECTRIC GASEOUS DISCHARGE DEVICE Ernst Friederlch, Berlln-Charlottenburg, Ger many, assignor to General Electric Company, a corporation of New York Application September 18, 1935, Serial No. 41,14 In Germany September 28, 1934 4 Claims.

The present invention relates to electric gaseous discharge devices, and particularly to devices of this type which are used as light sources.

A particular object of the invention is to provide a novel electric gaseous discharge device of high luminous efllciency. Another object of my invention is to provide a lamp which will emit a white light.

Still another object of my invention claimed.

It is well known that the radiations emitted by an incandescent body are a perature thereof, and that function of the tem-- in order to obtain a high luminous eiliciency in the visible part of the spectrum it is necessary to have a very high temperature. mentary type which are in In the incandescent lamps of the filacommon use various considerations provide practical limitations on the temperature which may be employed, however, and thus definitely limit the efliciency which may be attained with this type of lamp. In the first place, where a filament or other solid body is used to emit the incande temperature obviously must scent radiations, the lie below the melting point. Furthermore, in most cases this operating temperature must be far below the melting point, since the high melting point bodies have the property of vaporizing stron gly evenat temperatures considerably below their melting point. With the usual construction of the luminous bodies used in electric incandescent lamps, the change in their solid properties due to temperature also plays a very essential role. The luminous bodies tend to become soft and to change their shape. By the nature of the crystallization the solidity of the luminous body is also often reavoided as far as possible.

According to the presen of course, serious in t invention a novel lamp structure is provided in which the importance of these changes in the incandescent body at high temperatures is greatly minimized,

with the result that it is now practicable to operate the luminous body at a considerably higher temperature than has heretofore been consistent with a reasonable lamp life.

In my novel structure the luminous body is made the anode of an electric discharge and is heated by this discharge in a well known manner. According to the invention the active part of the anode or anodes consists of a number of wires or wire helices of high melting conductors such as tungsten, molybdenum, platinum, carbon, niobium carbide, tantalum carbide etc. which, with their free ends in the manner of a brush, stand opposite the cathode or cathodes. For this purpose the wires are thinher than 20 mu. With this construction the anode or anodes have been found to successfully operate at a temperature close below the melting point of the material from which the anode-wires or helices are made, since these glowing hot wires or helices are neither under tension nor do they have to carry a load. The small diameter of the wires reduces the energy loss due to heat abduction, and thus results in an increased efilciency. Vaporizing of the luminous body material which is so disturbing in the incandescent lamp art can play only a subordinate role here since the wires vaporize only from one end and thus are consumed gradually without suddenly becoming entirely useless due to burning through in the middie. With the gradual consumption of the wires, points of the same kind are always opposed to the cathode, and, given favorably chosen arrangements it is not disturbing that these points gradually recede from the cathode during operation. With the lamps according to the invention the tungsten or other particles which vaporize oil? are not as harmful as with the customary incandescent lamps, due to the presence of the discharge. In so far as the vaporized particles are positively charged they are conducted to the cathode, where they are harmlesaespecially with cathodes having a metallic surface such as thorium cathodes or caesium cathodes. In so far as the particles which vaporize off are charged negatively they are kept close to the anode by the electrons which occur in great number, and thus tend to prevent further vaporization, and many are conducted back to the anode. Finally, in so far as the particles which are vaporized off are uncharged, they are ionized by electrons at the high voltage and current density of the discharge and in this manner are also made harmless. For the small amounts of tungsten which vaporize off and which, at worst, still reach the bulb wall, a coating of getter substances which have a clearing up effect, for instance sodium chloride, cryolite and other, especially halogen-bearing, substances, is effective to prevent wall blackening.

For the purpose of illustrating my invention I u have shown several preferred embodiments thereof in the accompanying drawing, in which Fig. 1 is an elevationalview of the electrode arrangement used in my novel lamp,

Figs. 2 and 3 are similar views of different modifications of the structure shown in Fig. 1,

Fig. 4 is similar view of a further modification of the structure of Fig. 1,

Fig. 5 is a sectional view of the same structure taken on the line 55 of Fig. 4,

Fig. 6 is a similar sectional view of a modification of the device shown in Fig. 4,

Figs. 7 and 8 are respectively elevational and planviews of another modification of the device shown in Fig. 1, and

Fig. 9 is a plan view of still another modiflca tion of the device shown in Fig. 1.

Fig. 1 shows the stem of a lamp with a simple electrode construction, the usual enclosing envelope being omitted. Into the pinch I of the stem tube 2 three wires 3, l, and 5 are fused, of which only the wires 3 and '5 are connected with outer current conductors 6 and I. The wires 4 and 5 carry an indirectly heated, cylindrical cathode 8 which rises upward vertically from the stem tube I, 2, said cathode being preferably coated with an active thermionic material such as barium,

.thorium, caesium or the like. The wire 3, toward the top, passes over into a rod shaped part 9 which runs parallel with the cathode and on which are fastened a number of thin wires III which point toward the cathode, in the manner of a brush. The rod shaped part 9 and the relatively thin wires III, which for example consist of tungsten, or another of the substances previ ously mentioned, form the anode of the lamp. The wires III, arranged brushlike, have about the strength of the'usual incandescent lamp wires. .The one end II of the heater filament (not shown) which is positioned within the cathode 8 is attached to the support wire- 3 of the anode, while the other end I2 is attached to the wire 5 which is connected to the cathode 8. The lamp according to Fig. 1 can be operated on direct or alternating current.

Fig. 2 shows a similar construction with which, however, two anodes 9, II and 9', I0 stand opposite the cathode 8. Thewires I0, I0 of the anodes, arranged brushlike, are here somewhat displaced in relation to each other, for effect, so that the wires do not cover each other when viewed from the side.

If one wishes to achieve a better exploitation of the cathode and to reduce the influence of the wearing-off of the wires, then it is advantageous to surround the cathode with anode brushes on all sides as much as possible. If this arrangement becomes very dense than the radiation can emerge almost only in the direction of the axis of the anode cylinder. It is therefore effective to arrange the wires in such 'a manner that they do not cover each other in this direction. Such a construction is shown in Fig. 3. The indirectly heated, cylindrical cathode 8 is surrounded by a conical anode body I3 to the inner surface of which are aflixed a plurality of wires I! that project toward the cathode and are arranged like a brush. Of these wires only those which stand in the cross section plane are shown in the figure. The conical body I3 is blunted on the side toward the stem I, 2 and serves at the same time as a reflector, in order to project the light radiation in'the desired direction.

One can also get a one-sided radiation in the manner showfi in Figs. 4 and 5. On the pinch I of the stem tube 2 a plate shaped anode is fastened by the aid of two risers Ii, which anode consists of a number of parallel running metal strips I8 which are held by.two transverse strips I! of which the lower one is fastened to the risers II. Between these metal strips I8 and welded fast to them for example, are the anode wires II, arranged brushlike, which are heated to luminosity by the discharge. Close before the points of these wires there is located a directly heated cathode I9 consisting of a wire which has a serpentine-like course. The ends of the cathode wire I9 are welded to. two inleads 20 which are fused into the stem. tube pinch. I and the upper end of which is bridged by a strip 2|. The middle parts of the cathode wire. I9 are additionally held by hooks 22 fastened to the strip 2| and by hooks 23 fused into the pinch. With this arrangement parts of the anode, principally the metal strips I6, are in some cases constructed as a mirror. This lamp, like the other lamps according to the invention, is operated on either direc or alternating current.

In case it is desired the anode plate I6 of Figs. 4 and 5 is curved in order to obtain a better gathering of the light, as shown in Fig. 6. In this arrangement the wires I8 are disposed radially about the cathode wire I9 which forms an approximation of a cylindrical surface. I

With the directly heated cathodes such as are used, for instance, in the lamps according to Figs. 4, 5 and 6, the heater current, on alternating current, is conveniently taken from a transformer in order to reduce the potential drop from the beginning to the end of g the glowing cathode wire and in order to prevent discharges between the cathode parts. On direct current the luminous bodyof an electric incandescent lamp is wired ahead of the positive end of the cathode, which luminous body is in some cases housed inside of the lamp constructed according to the present invention. Such an external resistance can also be used to advantage with alternating current heating.

While as shown in the previous figures the anode surrounds the cathode, in. some cases the cathode surrounds the anode. 'I'he essential parts of such an arrangement are shown in Figs. 7 and 8. The anode rod 24 which is fused, into the stem tube pinch I carries the wires 25 which project uniformly on both sides and which, all together, form a cylindrical brush, as best shown in Fig. 8.. This anode is surrounded by v a directly heated, helically shaped filamentary cathode 26, which is carried by two supports 21, 28 which are fused into the pinch.

In each case this electrode is enclosed within a suitable envelope of glass or the like. This envelope can contain any suitable gaseous atmosphere, such as neon, argon, mercury, or the like, either alone or in combination at a suitable pressure, such as a few millimeters of mercury, or it may be entirely evacuated, as desired.

When any of these devices is connected to a suitable source of potential the cathode l, I! or 26 is heated and gives oi! electrons which support a discharge between said cathode and the brushlike wires Hi, It or 25, as the case may be, of the adjacent anode. These wires are heated by this discharge to an incandescent temperature which is materially higher than thelight emitted much more closely approaches daylight in color. The vaporization of the anode wires, even at this high temperature has been found to be very slight, due to the presence of the gaseous discharge, for the reasons which have been fully discussed hereinbefore. Furthermore the slight recession of these anode wires from the cathode as a result thereof only slightly alters the discharge. As a result it has been found that my novel lamp not only has a high luminous efllciency but also an exceptionaly long useful life.

It is especially advantageous for the lamps according to the invention to use a caesium cathode or to use of a caesium vapor filling which does not participate in the discharge and which removes the space charge, because thus the greatest electron current is obtained for the applied heater wattage. The caesium cathode also can be used as an indirectly or as a directly heated cathode.

As a special shape for the anode wires wire helices also come into consideration, the axis of which is pointed toward the hot cathode, as shown in Fig. 9 of the drawing. For reducing theheat losses it is advantageous to coil into a helix only that end part 29 of each wire In which is toward the cathode 8. Since the-helix, even if it is burnt off to a small remainder, prolies behind it against the electron current and will take up all the electrons itself, therefor the luminous body temperature rises toward the end of the operating life. With a correct proportioning of the separate parts of the lamp in relation to each other; this phenomenon entirely compensates for the slowly decreasing electron current density. p

In order to achieve a uniform loading of all the luminous body wires it is effective to surround the cathode with a space charge grid. Often it will also be advantageous to coat the wires, with the exception of the point, with an insulating substance as for instance, magnesium oxide, which burns on uniformly with the wire. Thus the result is obtained that the electrons are conducted onto the wire points exclusively and the latter are thereby brought to an especially high heat.

With the extremely high load capacity of the new lamps in comparison with those heretofore in use, the yield of ultra violet light is very much greater. For this reason the lamps according to the invention are also especially suitable for ultra violet radiation when an ultra violet transmittingbulb is used.

While I have illustrated my invention by reference to certain preferred embodiments thereof, it is to be understood that various changes, omissions and substitutions, within the scope of the appended. claims, can

- departing from the spirit of the invention.

direct the light from said wires in tects the straight part of the wire III which be made therein without What I claim as new and desire to secure b Letters Patent ofthe United States, is:

1. An electric lamp comprising a sealed envelope having elongated electrodes mounted therein, said electrodes having separate current leads; being substantially coextensive linearly and being mounted in opposing positions, one of said electrodes comprising a support member and a plurality of discreet, fine wires of a refractory conducting material affixed to and spaced along said support member, said wires extending toward and terminating adjacent the periphery of the other of said electrodes, each of said wires being coated with an insulating substance except at the end thereof adjacent said last named electrode.

2. An electric lamp comprising a sealed envelope having elongated electrodes mounted therein, said electrodes having separate current leads, being substantially coextensive liniearly and being mounted in opposing positions, one of said electrodes consisting of a support memher and a plurality of discreet, fine wires of a refractory conducting material ailixed to and spaced along said support member, said wires extending toward and terminating adjacent the periphery of the other of said electrodes, said support member having a reflecting surface to t a desired direction.

3. An electric lamp comprising a sealed envelope having caesium therein and having elongated, cooperating, main electrodes mounted therein, said main electrodes having separate current leads, being substantially coextensive linearly and being mounted in opposing positions, one of said main electrodes comprising a support member and a plurality of discreet, fine wires of a refractory conducting material affixed to and spaced along said support member, said wires extending toward and terminating adjacent the periphery of the other of said main electrodes, said wires being adapted to emit light by incandescence.

4. An electric lamp comprising a sealed envelope having elongated, cooperating, main electrodes mounted therein, said main electrodes having separate current leads, being substan: tially coextensive linearly and being mounted in opposing positions, one of said main electrodes having .a coating of caesium'thereon, another of said electrodes comprising a support member and a plurality of discreet, fine wires of a refractory conducting material afllxed to and spaced along said support member, said wires adjacent the extending toward and terminating periphery ofsaid first named main electrode, said wires being adapted to be heated to incandescence by electron bombardment thereof.

-ERNS'I'FRIEDERICB. 

